Pour 400 ml of water into a deep saucepan. Cover and poor over high heat. When start to boil add the potato, the carrot and the peas. Cover and cook about 12-15 minutes, until the potato cubes are soft. Dry and pour into a bowl. Add the cooked ham and the cheese. Add the salt, the black paper and dry oregano. Stir. Add the mayonnaise and stir well. Pour into a serving cup and refrigerate about 30 minutes before serving.